Process for the preparation of inorganic gels



March 8, 1960 R. H. CRAMYER ET AL PROCESS FOR THE PREPARATION OF INORGANIC GELS Filed March 28, 1956 iii.

ATTORNEY `been proposed.

United States .Patent PROCESS FOR THE PREPARATION or INORGANIC GELs Y Robert H. Cramer, Woodbury, NJ., and Albert Schwartz, Philadelphia, Pa., assignors to Socony Mob VOil Company, Inc., a corporation ofv New York Application March 28, 1.956, Serial No. 574,486 1o claims, `(clk. :sz-46s) f This application is ar-lcontinuation-in-part of our copending applicationSerial No.` 489,482, ledFebruary The invention described herein relates to an improved 'y process for the formation of porous adsorptive inorganic l gels. More particularly, the present invention is'concerned with the preparation of `hy'drogels Vhaving a solids content consisting essentially of a major proportion of alumina and a minor proportion of at least one other metal or metal oxide. ln. particular,` the invention'is directed to the vproduction of hydrosols and hydrogels characterized by a relatively high solids content, i.e.,

Patented Mar. 8, 1960 Y oxide or metal havinga solids content greater thanfabou't j 5% by Weight. A still further object is. the'pr'oduction ofquick-setting alumina-metal and alumina-metal oxide hydrosols capable of being manufcturedinto hardA gel spheroids in accordance With the above-noted wellknown methods. e v

The abovel and other objects'v which will bev'apparent to those skilled in the art are achievedinaccordance j with the present `invention wherein hydrogelsfconsisting essentially'of a major proportion of alumina and aV minor greater than about 5%- by weight, which hydrogels can l be subjected to subsequent wet processing operations with- 4 out effecting appreciable disintegration thereof.

Various methods for producing gels consisting essentially of a major proportion of alumina and a minor proportion of a metal or metal oxide have heretofore In many ofthe previously suggested processes for manufacturing suchgels, extensive washing of the hydrogel is required to remove impurities in order that the tinal product possess the desired properties. Such extensive washing has been detrimental to the yield of product since a considerable amount of hydrogel ordinarily undergoes disintegration during such step. While other processes have been developed wherein hydrosols are produced directly` in a substantially pure state and which do not require washing of the resulting hydrogel, these processes generally result in the formation of a hydrosol having'a solids content so low that considerable concentration must be eiected.l Such methods of preparation are accordingly* not well adapted for large scale manufacture of alumina-metal oxide or aluminametal gels since the handling of extremely large quantities of dilute solutions and the drying of hydrcgels of l low solids content are required. ln addition, such hydrcsols and the corresponding hydrogels produced therefrom, possessinga comparatively low solids vcontent have not been suitable for` the production of beadlike spheroidal gel particles by well known methods involving introduction of a hydrosol in the form of globules into a water-immiscible medium in which the sol globules set to hydrogel beads. Y

One of the principal objects of the present invention is the provision of a process for preparing `hydrogels gelatinous precipitates.

proportion of atleast oneother metal ormetal oxide are prepared by intimately admixing solutions ofan alkali metal aluminate, ajhydrcxy carboxylic' acid' or salt thereof, and an inorganicV waterfsoluble compound which, upon ysubsequent decomposition, furnishes the aforesaid metal ormetal oxidevThe reactant solutions are mined in controlled quantitiesrto yield an alumina metal or alumina-metal roxide sol which sets to anv allembracing precirnta'te'freev hydrogel. f

It is emphasized that the present process is directed to a method of preparing hydrogels as'distinguished from It has heretofore been taught that the presence of electrolyte salts i n an aluminalcontaining hydrogel forming mixture hafs the detrimental effect of coagulating'the aluminum ions inthe form of an irreversible gelatinous precipitate and not in thevv form of a true hydrogel. The gelatinous precipitates so pro'- pound of the metal which it is desired to cogelw'ithv alumina under the conditions hereinafter set forth does v`not serve to coagulate the reactants in the form of a gelatincus precipitate as would be expectedV from prior art teachings but, on the contrary, affords the formation of a hydrogel which can be subjected toextensive washing with distinctly less disintegration than a corresponding y hydrogel prepared in the absence of such electrolyte ccmpound.

` The present invention thus contemplates animproved method for preparing hydrogels consisting essentially of a major proportion of alumina and a minor proportion of other metal oxide or metal which,.whenvdried, yield porous adsorptive alumina-metal or metal oxide gels. In order to produce such hydrogels having a high abamos Y solids content and capable of being subjected to subsequent wet processing operations without undergoing disintegration, it has been discovered that certain critical conditions must be observed during formation. It has been found that a stable hydrogel of alumina and other metal or metal oxide component having a short time of set and a high solids content may readily be prepared by mixing aqueous solutions of an alkali metal aluminate, a hydroxy carboxylic acid or salt thereof, and an inorganic water-soluble compound which, upon subsequent decomposition, furnishes said component and controlling the ratio equivalents of total inorganic anion to total alkali metal and the ratio equivalents of hydroxy carboxylic acid anion to total metal in the reaction mixture undergoing complex formation with hydroxy carboxylic acid anion. Metals whichY can be complexed with hydroxycarboxylic anions include, among others: aluminum, chromium, iron, cobalt, manganese, nickel, calcium, titanium, antimony, tin, lead, copper, boron, and molybdenum. Generally, hydrogels prepared by the process describedherein are characterized by a gelation time of not more than 2 hours and a solids content of between about 5 and about 30% by weight, although it is to be realized that hydrogels having a longer time of set and a lesser solids content when desired may also be produced by the present method. The method of this invention is particularly suitable for the production of hydrogels characterized by a time of set in the range of 0.5 to 300 seconds.

`'Ihe particular ratio equivalents above-described contained in the reaction mixture will depend upon the exact nature of the alumina-metal oxide or alumina-metal hydrogel desired. These ratio equivalents may be readily` ascertained by those skilled in the art following the principles of this invention. Temperature, pl-I, and solids content are interrelated Variables eifecting gelation and, Within the limits in which formation of hydrogels occurs, they control gelation time. In general, the other factors can be controlled to achieve gelation at any practical solution temperature. The pH of the hydrogel should generally be maintained on the alkaline side, i.e., above about 7. In particular, it is preferred that the pH of the hydrogel be within the approximate range of 10.5 to 12.5.

As the alkali metal aluminate reactant, lithium, sodium, or potassium aluminate will generally be employed, although it will be realized that aluminates of other alkali metals may also be effectively used. Of the alkali metal aluminates, sodium aluminate is accorded preference for use in the present process. An aqueous solution of the `alkali metal aluminate is preferably used. It is generally desirable to add to the solution a small amount of the corresponding alkali metal hydroxide to stabilize the aluminate solution.

Representative but non-limiting examples of the hydroxy carboxylic acids employed are glycolic, lactic, citric, tartaric, gluconic, malic, beta hydroxy butyric, beta hydroxy propionic, glyceric, and salicylic acids. It is preferred to employ an acid in which the hydroxy group is not more than two carbon atoms removed from the carboxyl group. Thus, in the case of aliphatic acids, alpha and beta hydroxy carboxylic acids are preferred. ln the case of cyclic or aromatic acids, orthocarboxylic acids are preferred. Salts of the foregoing acids may also be employed, particularly alkali metal and arnmonium salts, it being understood that it is essential, in accordance with the instant process, that a hydroxy carboxylic acid anion bepresent in the hydrosol-forming mixture and that such anion may be introduced from the acid or from salts thereof.

The inorganic water-soluble compound employed containing metal other than aluminum is generally a salt Y 'Iii in aqueous solution will be employed. The mineral acid salts of the metal which it is desired to cogel with alumina are typical representative compounds and include the nitrates, sulfates, and chlorides of various metals. It is also contemplated that water-soluble acids or salts containing metals which it is desired to cogel with the alumina may be employed, such as chloroplatinic acid, chloropalladic acid, brornoplatinic acid, ammonium chloroplatinate, etc. Elcctrolytic water-soluble compounds of a multitude of metals may be suitably employed in the present process, particularly including those of groups I-B, II, III, IV, VI, VII, and VIII of the periodic table. Typical water-soluble compounds for use in the process described herein are those of beryllium, chromium, cobalt, boron, manganese, molybdenum, iron, nickel, silver, tin, magnesium, titanium, tungsten, platinum, zirconium, rhodium, vanadium, zinc, and palladium.

The foregoing reactant solutions are intimately admixed in any desired manner to yield a resultant hydrosol. rlhus, the inorganic water-soluble compound containing metal other than aluminum may be initially added in whole or part so that no precipitation is effected to either the hydroxy carboxylic acid solution or the alkali metal aluminate solution prior to mixing the two latter solutions. The solutions may be intimately admixed by flowing streams thereof together under conditions of rapid flow such as in a mixing nozzle. The reactants may be in the form of individual streams or, after initially adding the inorganic metal-containing compound to one reactant solution, the latter may be mixed with the other reactant solution.

It has been found in accordance with the instant invention that a stable hydrogel consisting essentially of a major proportion of alumina and a minor proportion of other metal-containing component either in the form of a metal or oxide thereof can be produced by controllingy the ratio of equivalents of the total inorganic anion to total alkali metal and the ratio of equivalents of hydroxy carboxylic acid anion to the total complexed metal, i.e., the combined equivalents of aluminum and other metal complexed by the hydroxy carboxylic acid anion contained in the hydrosol forming solutions. The accor. panying drawing presents data graphically, illustrating relationships between the aforesaid ratio equivalents satisfactory for the formation of the desired hydrogels.

Referring more particularly to the drawing, itwill be seen that the ratio of equivalents of inorganic anion to equivalents of alkali metal is desirably between about 0.005 and about 0.2 and the ratio of equivalents of hydroxy carboxylic acid anion to the total complexed metal is within the area ABCD. Preferably, the ratio of equivalents of inorganic anion to equivalents of total alkali metal is between about 0.05 and about 0.1 and the ratio of equivalents of hydroxy carboxylic acid anion to equivalents of total complexed metal is within the area EFGH. Hydrogels having the latter equivalent ratio characteristics are particularly resistant to disintegration upon washing or otherwise wet processing.

The hydrosol formed in accordance with the present process is characterized by an inherent capacity to set to a hydrogel upon lapse of a suitable period of time without addition to or subtraction from the hydrosol of any substance. The resulting hydrogel may be allowedto set in the form of a mass which is thereafter broken up or cut up into particles for wet processing. An alternate method for preparing the hydrogel particles is to drop the hydrosol in the form of globules into a column of water-immiscible liquid so that spheroidal bead-like particles of hydrogel are formed upon gelation of the hydrosol globules while maintainedy inthe liquid.

The particles of hydrogel, after formation, are suitably, but noty necessarily, aged in a water-immiscible media suc'n as oil at an elevated temperature above about 100 F. for between about l and about 48 hours. vHydrogel containing a majory proportion of alumina `formed in accordance with the above-described method is generally i subject to a loss of aluminum as alkali metalraluminate if immediately Washed with water. Thstends'to weaken the hydrogel to such an extent that it becomes susceptible to disintegration in the wash water. Such adverse eect can'be avoided by treating the freshly formed aluminacontaining hydrogel with an aqueous solution having a pH of greater than 4 but less than the pH of the hydrogel.l A suitable representative treating medium is an am- Vmonium salt solution, f or example, solutions of'ammonicination Awill depend, in part, on the use to be made of` The washed .hydrogel can be satisfactorily dried in either superheate'd'steani or heated air.' The'hydr'ogel so dried may thereafter be' calcinediat an elevated temperature" generally within the approximate range of 350 F. to 1400 F. The-particular temperature chosen for calthe finished gel. Thus, where the gel is to be employed about SOO Randabout 1400 v following reactants:

other hand, if the pH is less than 4, the solubleanions become more difcult to wash out. it has been found advisable to maintain a solution of the aforementioned pH range in contact with vthe freshly formed alumina-containing hydrogel for some time after formation.' Forexample, thek solution is suitably recirculated through the fresh hydrogel for 2. to 48 hoursV after forming in order!" to iix thealumina.

The'hydrogel may thereafter be Washed with water or water containing a small amount of electrolyte to prevent the alumina from peptizing. lf theY salt used for treating decomposes upon heating, the hydrogel may be partially Washed to remove soluble ions which do not decompose upon heating and the remainder of the impurities removed by tempering.f

Thus, the alkali metal ionfrom the aluminate solution may be replaced by treating in a concentrated saltsolution. Additional components may be introduced into the gel by ion exchange during this step. The salt may be one which decomposes upon heating, such as NH4NO3, 'or a salt such as (NH4)2SO4, vwhich introduces a nonmetallic ion which can be washed out or removed upon heating or a polyvalent metal salt which will introduce as an adsorbent, it is calcined at a temperature in the approximate range of 350TF. to 800 F. If on the other hand, the gel is to be usedas a catalyst or catalyst support, the temperature of calcination-is generally between The invention may be limitingexamples:

illustrated byythe followingnon- EXAMPLE 1 An Y alumina-chromia hydrogelv w Solution A: VSodium aluminate solution ,having a speciiic gravity at" 60 F. 'of 1,7395, containing by weight 29.6% sodium aluminate, 5.0%" sodium hydroxide,V and 65.4% water. vSolution B: Acid solution having `a .specic gravity at 60.F of 1.229 and containing by weight`38.0%= citric acid, 10.5% chromium nitrate, [Cr(`NO3)3-9H2O] and 51.5% Water. v w

Solution A` owing-ata rate of 580 cc./min.was mixed in av nozzle with Solution B, ilowing ata rate of Y288 cc./min. The hydrosolso formed, having'a concentration of :188 grams A12O3-Cr203 per liter was .poured into a trayv and set thereinat a temperature of 140 F. toa'hydrogel in less than 1 second. The resulting hydrogelr was hard and had a pH of 12.2.- The ratio of equivalents of-nitrate tojequivalents ofsodium wasV i 0.071 andthe ratio of equivalents of citric acid to equivalents of metalcomplexed (aluminum and chromium) the hydrogel. The hydrogel did not undergo any disina metal ion into the gel structure. Also, additional components maybe introduced into the hydrogel during the base exchange operation. Likewise, additional components may be introduced by impregnation during the hytegration during the foregoing wet processing steps.. The washed material was then dried in steam at 23S-325 F.

- for 51/2 hours and then calcined=2v hours at l000 F. in air. The resulting gel has a surface area of 362 square drogel stage or by impregnation of the dried and/or calmeters per gramand contained approximately 5.8 weight percent of chromia andl approximately 94.2;weight percentof alumina.

Examples 2 to 8, employing various inorganic watersoluble metal compounds, hydroxy carboxylic acids, and alkali metal aluminates, carried out following .the general procedure of Example 1, are set forth in Table IYbelow'r Table I Forming Alkali metal aluminate solution Acid solution Ex. y Y v No. Alkali metal Alkali metal Metal compound Acid nluminate hydroxide H2O, Spgr. Rate, H2O, Sp.gr.y Rate,

percent cc./ percent 60 Vcc./ weight F. min weight F. min. Type Percent Type Percent Type Percent Type Percent Weight Weight weight weight 2, NaAlOi 29.6 NaOH 5.0 r65.4 1.395 580 tdgNOs 12.6 Citric 35.8 Y 5l.6 1.304 310 3.- NuAlOz 29.6 NaOH 5.0 65.4 1.395 580 .g(NOa)2-6H2O 10.1 lo- 38.3 51.6 1.2l7 l308 4 Na A10, 29,6 Naot; 5,0 55.4 1.394 20o {ffol 055:;7 ..d0 43.2 52.6 1.235' se 5 KAlOg 35.4 KOH 7.2 i 57.4 1426 200 T Glyc0lic 36.4 53.2 1.180 127 6 KAlO: 35.4 KOH 7.2 57.4 1.426 200 {(NIOMWOHZO: 5:0 }Lactic .L 45.0 45.1 1.190 120 7 NaAlOn v 29.6 NaOH 5.1 65.3 1.402 184 ZrOCli-SHzO 10.4 Tartaric 35.6v '54.0 1.254 110 8 NaAlOz 29.6 NaOH. 5.1 65.3 1.402 184 Mn(NO3)2-6H2O 9.4 Anrrnoliumr 41.6 49.0 1.247 112 ci ra e.

11s-prepared from the Table I-Continued Hydrosol propertiesV Processing Gel properties Equiv- Base exchange Composition (approx. alents of Equivin 20% weight Drying Weight percent) Ex. Grams hydroxyalents of N HlNOa Water Sur- No. metal carboxylic inorganic wash, face Time, Temp., pH oxide acid anon/ anion/ dur- (Sqseo. F. per equivequivation meters] liter alents of alents of Durin hrs. Temp., Time gram) hydrosol total alkali pH ation F. (hrs.) Analyzed complexed metal in hrs.

metal 2 0. 5 135 11. 9 246 0.228 0.076V 6. 4 24 168 23S-325 51/2 361 AgzO, 1.8%... A1202, 98.2. 3 0. 5 140 175 0. 226 0.075 7.0 24 336 235-325 512 358 MgO, 3.6%... A1203, 96.4. 4 20 136 1l. 5 181 0 21 0.067 6. 2 2-1 V144 235 Y 5A; 321 Pt, 0.2%----- A1201, 09.8.

Calculated 6 2-3 144 12. 4 184 0. 229 0.069 7-10 24 G2 235 9 B203, 11.2%-- A1203, 88.2. e 1 124 12.1 19o 0.225 0.064*- 7-10 24 127 235 s @125: }Ai2oa,rs7.. 7 1 18 150 12.0 y 181 0.220 0.072 7-10 24 38 235 9 ZrO2, 10.4%.. A1203, 89.6. 8- 1 95 12.1 172 0. 228 0. 072 7-10 24 86 235 9 M110, 6.3%-. A1203, 93.7.

1 Hours.

It will be seen from the above table that alumina-metal oxide and alumina-metal gels may be prepared in accordance with the present procedure utilizing an alkali metal aluminate, hydroxy carboxylic acid or salt thereof, and water-soluble metal compound system with a wide variety of reactants. Thus, the desired gels were formed using citric acid (Examples l to 4), glycolic acid (Example 5), lactic acid (Example 6), tartaric acid (Example 7), and a hydroxy carboxylic acid salt, i.e., ammonium citrate (Example 8). Gels were formed containing alumina and a metal component of metals of groups I B (Example 2), II (Example 3),- III (Examples 4 and 5), IV (Example 7), VI (Examples 1 and 6), VII (Example 8), and Vlll l (Examples 4 and 6) of the periodic table. Gels were also formed by cogelling with alumina one or more metal components. Thus, Examples 4 and 6 illustrate the use of two metal-containing compounds for reaction with alkali metal aluminate and hydroxy carboxylic acid solutions. All of the gels prepared following the teachings of this invention were resistant to disintegration upon wet processing. In contradistinction, comparable preparation of an alumina-containing hydrogel formed by reaction of an alkali metal aluminate and a hydroxy carboxylic acid without any added water-soluble metal compound yielded a hydrogel which underwent considerable disintegration upon wet processing, indicating that the presence of added metal-containing compound in the reaction mixture is essential in obtaining a resulting alumina-containing hydrogel 'which does not undergo appreciable disintegration upon extended contact thereof with aqueous media.

It is contemplated that the alumina-metal and aluminametal oxide gels produced in accordance with the process of this invention may be used as desiccants, adsorbents,

treating, refining or purifying agents, or as a catalyst sup-Y port, catalyst or Acomponent of a catalyst for the conversion of organic compounds and particularly the conversion of hydrocarbons. Thus composites of alumina with other metal oxides and metals have been widely employed as catalysts in cracking, reforming, and desulfurization of petroleum hydrocarbons. Alumina-containing catalysts have also been used in hydrogenation, oxidation, and dehydration reactions. Typical alumina-containing cracking catalysts include composites of boriaalumina, zirconia-alumina, and beryllia-alumina. forming catalysts include composites of chromia-alumina, molybdena-alumna, and platinum-alumina. One commercially employed desulfurization catalyst is made up of a composite of cobalt oxide, molybdena, and alumina. Composites of alumina and silver are useful in catalytically promoting oxidation reactions. Likewise, catalytic composites of alumina with various other metals and metal oxides as indicated Vhereinabove maybe prepared,

in accordance with the process of this invention. Also, it is contemplated that other constituents may be incorporated in the hydrosol, hydrogel or impregnated on the finished gel product produced in Vaccordance with the Amethod described herein. Such catalysts are particularly valuable in the form of hard spheroidal particles since they are thereby rendered more resistant to abrasion and and are hence well adapted to either static or movingbed type hydrocarbon conversion systems wherein the catalyst moves in a closed path, including a reactor and a regenerator.

AIt is to be understood that the above description is merely illustrative of preferred embodiments of the invention, of which many variations may be made by those skilled in the art Without departing from the spirit thereof.

We claim:

l. A process for preparing an inorganic gel consisting essentially of a major proportion of alumina and a minor proportion of at least one other component selected from the group consisting of a metal and metal oxide, which comprises forming a hydrosol characterized by an inherent capacity to set to a hydrogel upon lapse of a suitable period of time by intimately admixing aqueous solutions of an alkali metal aluminate, an inorganic watersoluble, metal-containing compound which, upon subse- -quent decomposition, furnishes said component and a compound selected from the group consisting of a hydroxy carboxylic acid and salts thereof in such proportions as to yield an alkaline hydrosol in which the ratio equivalents of total inorganic anion to total alkali metal is between about 0.005 and about 0.2 and the ratio equivalents of hydroxy carboxylic acid anion to complexed metal is within the area ABCD ofthe accompanying drawing, maintaining the resulting hydrosol without addition to or subtraction fromsaid sol of any substance until the same sets to a hydrogel, treating the resulting hydrogel with an ammonium salt solution having a pH in the approximate range of 4 to 10 for a period of at least two hours, washing .the treated hydrogel free of water-soluble impurities, and drying.

2. A process for preparing an inorganic gel consisting Vessentially of a major proportion of alumina having a minor proportion of at least one other metal oxide, which comprises forming a hydrosol characterized by an in-l herent capacity to set to a hydrogel upon lapse of a suitable period of time by intimately admixing aqueous solutions of an alkali metal aluminate, a metal mineral acid salt which, upon subsequent decomposition, furnishes said metal oxide and a compound selected from the group Y consisting of a hydroxy carboxylic acid and salts thereof to yield a hydrosol having a pH between about 10.5 and about 12.5 and a solids content between about 5 and 6. A process for'preparing an'inorganc'g'l consisting `essentially of a major proportion of alumina and a minor proportion of platinum, which comprises forming a hydrosol characterized by an 4inherent capacity to set to a hydrogel upon lapse of a suitablev period of time by intimately admixing aqueous solutions of an alkali metal from said sol of any substance until the same sets to a Y hydrogel, washing the resulting hydrogel free of watersoluble impurities, and thereafter drying.

3. A process for preparing an inorganic gel consisting essentially of a major proportion of alumina and a minor proportion of at least one other component seleoted'from the group consisting of a'metal and metal oxide, which comprises forming a hydrosol characterized by an inherent capacity toA set toav hydrogel upon, lapse of a suitable period of time by intimately admixing aqueous aluminate, chloroplatinic acid, and a compound selected from the group consisting of a hydroxy carboxylic acid and salts thereof in such proportionsas to .yield an alkaline hydrosol in which the ratio equivalentsl of total inorganic anionskto total alkali metal is between about 0.005 and about 0.2 and the ratio equivalents of hydroxysolutions of an alkali metal aluminate, an inorganic water-soluble, metal-containing compound which,` upon subsequent ,decornposition, furnishessaid component and aY compound selected from the group consisting of a hy droxy carboxylic acid and salts thereof in such proportions as to yield an alkaline hydrosol in which the ratio equivalents of theanion of said metal-containing compound to alkali metal-,is between about 0.05 and about 0.1 and the ratio equivalents of hydroxy carboxylic acid anion to complexed metal is within the area EFGH of the accompanying drawing, maintaining the resulting hydrosol without addition to or subtraction from said sol of any substance until the same sets to a hydrogel,'treating the resulting hydrogel withan ammonium saltV solution having a pH in the approximate range of 4 lto l0 for a period of at least two hours, washing the treated hydrogel free of water-soluble impurities, anddrying.

4. A process for preparing an inorganic gel consisting essentially of a major proportion of alumina having a minor proportion of at least one other metal oxide, which comprises forming a hydrosol characterized by an inherf ent capacity to set to a hydrogel upon lapse of a suitable period of time by intimately admixing aqueous solutions lof an alkali metal aluminate, a metal mineral acid salt which, upon subsequent decomposition,Y furnishes said metal oxide and a compound selected from the group consisting of a hydroxy carboxylic acid and salts thereof to yield a hydrosol having a pH between about 10.5 and about v12.5 anda solids content between about 5 and about30 percent by Weightand in which the ratio equivalents `of metal salt anion to alkali metal is between about carboxylic acid anionto complexedaluminum and platinum isvwithin the area ABCDof the accompanying drawing, maintaining the resulting hydrosol without addition to or subtraction fromsaid sol of any substance until vthe same sets to a hydrogel, treating the resulting hydrogelwith an ammoniumsalt solution having a pH in the approximate range of 4 to l0 for a period of at least two hours, Washing theV treated hydrogel free of water-soluble impurities, and drying.

7. A process for preparing an inorganic gel consisting y essentially of a major proportion of alumina and a minor I vproportion of molybdena, which comprises forming a hydrosol characterized by an inherent capacity to set to a hydrogel upon lapse of a suitable period of time by intimately admixing an aqueous solution 4of an alkali metal aluminate, and inorganic water-soluble molyb- Ydenum salt, and a compound selected from the group and the ratio equivalents Aof hydroxycarboxylic acid anion 0.05 and about 0`.l and the ratio equivalents of hydroxy carboxylic acid anion to complexed metal is within'the area EFGH of the accompanying drawing, maintaining the resulting hydrosol without addition to or subtraction from said sol .of any substance until the same sets to a hydrogel, washing the resulting hydrogel free of watersoluble impurities, and thereafter drying.

S. A process for preparing an inorganic gel consisting essentially of a major proportionof alumina and a minor proportion of chromia, which Vcomprises forming a hydrosol characterized by an inherent capacity to Vset to a hydrogel upon lapse ofa suitable period of time .by' intimately admixing an aqueous solution of an alkali metal aluminate, an inorganic `vfvater-soluble chromium` salt, and a compound selected from the-group consisting of a hydroxy carboxylic acid and salts thereof in such proportions as to yield an alkaline hydrosol in which the ratio equivalents of total inorganic anions to total. alkali metal is between about 0.005 and about 0.2 and the to complexed aluminum and molybdenum is Within Vthe,

area ABCD of the accompanying'drawing, maintaining the resulting hydrosol without addition to or subtraction from saidsol of any substance until the same sets to a hydrogel, treating the resulting hydrogel with an ammonium salt solution having a pH in the approximate range of 4 to l0 for a period of at least two hours, washing the treated hydrogel free of Water-soluble impurities, and drying.

8. A process for preparing an inorganic gel consisting essentially of a major proportion of alumina and a minor proportion of silver oxide, which comprises forming a hydrosol characterized by an inherent capacity to set to a lhydrogel upon lapse of a suitable period of time `by intimately admxing an aqueous solution of an alkali metal aluminate, an inorganic Water-soluble silver salt, andv a compound selected from the group consisting of a hydroxyl carboxylic acid and salts thereof in such proportions as to yield an alkaline hydrosol in which the ratio equivalents of total inorganic anions to total alkali metal. is between about 0.005 and about 0.2 and the hydrosol without addition to or subtraction from said sol of anysubstance until the same sets to a hydrogel, treating the resulting hydrogel with an ammonium salt solution having a pH inthe approximate range of 4 to 10 for a period of at least two hours, washing the treated hydrogel free of water-soluble impurities, and drying.

9. A process for preparing an inorganic gel consisting essentially of a major proportion ofv alumina and a minor proportion,v of the oxides of cobalt and molybdenum, which comprises forming-.a hydrosol characterized byan inherentcapacity to set to ra. hydrogel upon lapse oi a suitable period of time byint'imat'ely admixing an aqueous" solution ofv an alkali metal aluminate, inorganic Water-soluble salts of cobalt and molybdenum, and acompound selected from the groupl consisting of a hydroxy `carboxylic acid and salts thereof in such proportions as to yield an alkaline hydrosol in which the ratio equival aeaaeoa lents of total inorganic anions to total alkali metal is between about V0.005 and about 0.2 and the ratio equivalents of hydroxycarboxylic acid anion to complexed aluminum, cobalt and molybdenum is within the area ABCD of the accompanying drawing, maintaining the resulting hydrosol without addition to or subtraction from said sol of any substance until the same sets to a hydrogel, treating the resulting hydrogel with an ammonium salt solution having a pH in the approximate range of 4 tc l0 for a period of at least two hours, washing the treated hydrogel free of water-soluble impurities, and drying.

10. A process for preparing an inorganic gel consisting essentially of a major proportion of alumina and a minor proportion of at least one other component selected from the group consisting of a metal and metal oxide, which comprises forming a hydrosol characterized by an inherent capacity to set to a hydrogel upon lapse of a suitable period of time by intimately admixing aqueous solutions of an alkali metal aluminate, an inorganic water-soluble compound which, upon subsequent decomposition, furnishes said component, and a compound selected from the group consisting lof a hydroxycarboxylic acid and salts thereof in such proportions as to yield an valkaline hydrosol'in which the ratio equivalents of total inorganic. anion to total alkali metal is between about 0.005 and about 0.2 and the ratio equivalents of hydroxycarboxylic acid anoin to complexed metal is Within the area ABCD of the accompanying drawing, maintaining the resulting hydrosol without addition to or subtraction from said sol of any substance until the same sets to a hydrogel, washing the resulting hydrogel free of water-soluble impurities, and drying.

References Cited in the iile of this patent UNITED STATES PATENTS 2,762,783 Kimberlin et al Sept. 1l, 1956 2,769,688 Milliken et al. Nov. 6, 1956 2,773,839 Stover et a1 Dec. 11, 1956 2,773,845 Stover et al Dec. 11, 1956 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,927,902 March 8, 1960 Robert H. Cramer et al.,

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected belo I Column 2, line 28, for of preparing" read for' preparing column 6, line 2l, for "1,395" read 1.895 --g line 47, for "has'l read had columns 5 and 6, Table I,

ninth column thereof, under the heading nMetal compound" and subheading "Type", fifth line, for "Na2B4O, JOI-120" read Na2B4O7. 10H20 --5 column l7 and 8, Table I-Continued thirteenth column thereof, under the heading "Gel properties" for the subheading "Surface (Sq, meters/gram" read Surface Area (Sq. meters/gram) column lO', line 28, for "and inorganic" read an inorganic Signed and sealed this 13th day of September 1960.

(SEAL) Attest: e j

KARL H. AXLINE ROBERT C. WATSON Attesting `Officer Commissioner of Patents 

1. A PROCESS FOR PREPARING AN INORGANIC GEL CONSISTING ESSENTIALLY OF A MAJOR PROPORTION OF ALUMINA AND A MINOR PROPORTION OF AT LEAST ONE OTHER COMPONENT SELECTED FROM THE GROUP CONSISTING OF A METAL AND METAL OXIDE, WHICH COMPRISES FORMING A HYDROSOL CHARACTERIZED BY AN INHERENT CAPACITY TO SET TO A HYDROGEL UPON LAPSE OF A SUITABLE PERIOD OF TIME BY INTIMATELY ADMIXING AQEOUS SOLUTIONS OF AN ALKALI METAL ALUMINATE, AN INORGANIC WATERSOLUBLE, METAL-CONTAINING COMPOUND WHICH, UPON SUBSEQUENT DECOMPOSITION, FURNISHES SAID COMPONENT AND A COMPOUND SELECTED FROM THE GROUP CONSISTING OF A HYDROXY CARBOXYLIC ACID AND SALTS THEREOF IN SUCH PROPORTIONS AS TO YIELD AN ALKALINE HYDROSOL IN WHICH THE RATIO 